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Question
From a point on the ground 40m away from the foot of a tower, the angle of elevation of the top of the tower is 30 . The angle of elevation of the top of a water tank (on the top of the tower) is 45 , Find (i) the height of the tower, (ii) the depth of the tank.
Solution
Let BC be the tower and CD be the water tank.
We have,
AB = 40m, ∠BAC = 30° and ∠BAD = 45°
In ΔABD,
` tan 45° = (BD)/(AB)`
`⇒ 1 = (BD)/40`
⇒ BD = 40 M
Now, in Δ ABC
`tan 30° = (BC)/(AB)`
`⇒1/ sqrt(3) = (BC) /40`
`⇒ BC = 40/sqrt(3)`
`⇒ BC = 40/ sqrt(3) xx sqrt(3)/sqrt(3)`
`⇒ BC = (40sqrt(3) )/3 m`
`"(i) The height of the tower," BC = (40 sqrt(3))/3 = (40 xx 1.73)/3 = 23.067 ~~ 23.1 m`
`"(ii) The depth of the tank " CD = (BD - BC) = (40-23.1 ) = 16.9 m`
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